1. Field of the Invention
The present invention relates to an electro luminescence display device, and more particularly to an electro luminescence display device that is adaptive for preventing the deterioration of an organic light-emitting layer by ultraviolet ray in a sealing process.
2. Description of the Related Art
Recently, there have been highlighted various flat panel display devices that are capable of reducing their weight and bulk which are disadvantages of a cathode ray tube (CRT). Such flat panel display devices include a liquid crystal display (LCD), a field emission display (FED), a plasma display panel (PDP) and an electro-luminescence (EL) display, etc.
The EL display in such display devices is a self-luminous device that makes a phosphorous material to emit light by a re-combination of electrons and holes. The EL display device is generally classified into an inorganic EL device using an inorganic compound as the phosphorous material and an organic EL using an organic compound as the phosphorus material. Such an EL display device has many advantages of a low voltage driving, a self-luminescence, a thin-thickness, a wide viewing angle, a fast response speed, a high contrast and so on such that it has been highlighted as a post-generation display device.
The organic EL device is comprised of an electron injection layer, an electron transport layer, a light-emitting layer, a hole transport layer and a hole injection layer. In such an organic EL device, when a predetermined voltage is applied between an anode and a cathode, electrons generated from the cathode move to the light-emitting layer through the electron injection layer and the electron transport layer, while holes generated from the anode move to the light-emitting layer through the hole injection layer and the hole transport layer. Accordingly, the electrons and the holes fed from the electron transport layer and the hole transport layer are re-combined to emit light.
Referring to FIG. 1, an EL display device of prior art includes a transparent substrate 2, an organic light-emitting layer 18 formed on the transparent substrate 2, a packaging plate 24 to seal off the organic light-emitting layer 18 on the transparent substrate 2, and a sealant 22 to bond the packaging plate 24 with the transparent substrate 2.
The organic light-emitting layer 18 includes an electron injection layer, an electron transport layer, alight-emitting layer, a hole transport layer and a hole injection layer that are deposited between an anode and a cathode (not shown). In the organic light-emitting layer 18, if voltage is applied between a transparent electrode as the anode and a metal electrode as the cathode, the electrons generated from the cathode move to the light-emitting layer through the electron injection layer and the electron transport layer, and the holes generated from the anode move to the light emitting layer through the hole injection layer and the hole transport layer. Accordingly, in the light-emitting layer, the electrons and the holes supplied from the electron transport layer and the hole transport layer collide with each other to be recombined, thereby generating light. The light is emitted to the outside through the anode, the transparent electrode, to display a picture.
The packaging plate 24 absorbs moisture and oxygen in the air, so a hygroscopic film 27 is stuck to the packaging plate 24 in order to protect the organic light-emitting layer 18 from the moisture and oxygen in the air. For this, the packaging plate 24 includes a stepped part 30 having an incline plane 26 and a horizontal plane. The stepped part 30 provides an inner space, where the hygroscopic film 27 is stuck, in the central part of the packaging plate 24.
The sealant 22 is spread between the transparent substrate 2 and the most outer stepped plane 28 of the packaging plate 24, and then it is hardened by illuminating it with ultraviolet rays, thereby bonding the packaging plate 24 with the transparent substrate 2. The packaging plate 24 seals up the organic light-emitting layer 18 by being bonded with the transparent substrate 2 by the sealant 22 in a vacuum state.
The electro luminescence display device of the related art, as shown in FIG. 2, bonds the transparent substrate 2 with the packaging plate 24 by a bonding device.
More specifically, the bonding device includes a large transparent substrate 2 where a plurality of organic light-emitting layers 18 are formed and which is fixed by a fixing means (not shown); a plurality of absorbers 50 to which a plurality of packaging plates 24 are absorbed, wherein the packaging plates 24 are bonded with the transparent substrate 2; a sealant 22 spread at the edge of the transparent substrate 2 or the packaging plate 24; an UV illuminating device 60 to illuminate an ultraviolet ray 62 to the sealant 24; and a mask 64 to mask other area than the sealant 24 in order that the ultraviolet ray 62 is not illuminated onto each organic light-emitting layer 18.
The absorbers 50 absorb the packaging plate 24 supplied from the outside, using a pad 52.
The absorber 50 has the packaging plate 24 absorbed on a pad 52 thereof and has the transparent substrate fixed thereto by a fixing means to align the organic light-emitting layer 18 formed on the transparent substrate 2 and the packaging plate 24.
And then, the ultraviolet ray 62 from the UV illuminating device 60 is illuminated onto the sealant 22 spread between the transparent substrate 2 and the packaging plate 24 for a designated time. At this moment, the mask 64 allows the ultraviolet rays 62 illuminated from the UV illuminating device 60 to be illuminated only on the sealant 22 spread between the transparent substrate 2 and the packaging plate 24, and the ultraviolet ray 62 is intercepted at the remaining areas.
Accordingly, the sealant 22 is hardened by the ultraviolet ray 62 illuminated through the mask 64 to bond the transparent substrate 2 with the packaging plate 24.
During the bonding of the transparent substrate 2 with the packaging plate 24 the ultraviolet rays 64 are illuminated onto the sealant 22 through the mask 64, as shown in FIG. 3. However, some ultraviolet rays 64 are reflected by the incline plane 26 of the stepped plane 30 formed at the packaging plate 24 to generate a reflected light 70. That is, the ultraviolet ray 64 is illuminated onto the sealant 22 to harden the sealant 22, and at the same time, is dispersed by the incline plane 26 of the stepped part 30 formed at the packaging plate 24 to generate the reflected light 70. The reflected light 70 may even be reflected over and over between the transparent substrate 2 and the incline plane 26 and the stepped plane 28 of the stepped part 30 of the packaging plate 24. This reflected ultraviolet light can illuminate onto the surrounding area of the organic light-emitting layer 18 of the EL display device. This reflected light 70 illuminated on to the organic light-emitting layer 18 deteriorates the organic light-emitting layer 18, and in addition, is illuminated onto the surrounding areas of the EL display device to change the characteristics of the driving devices, such as the transistor of the surrounding circuit of the EL display device.
Accordingly, the EL display device of related art has the edge of the organic light-emitting layer 18 deteriorated by the reflected light 70 which is caused by the reflection/dispersion of ultraviolet rays 64 illuminated onto the sealant 22 during the bonding process of the transparent substrate 2 and the packaging plate 24. Further, the reflected lights can change the characteristics of the driving devices of the surrounding circuit, thereby causing a brightness difference between the central part 80 of the EL display device and the other areas 82, as shown in FIG. 4.